1. Field of the Invention
The present invention relates to a photoelectric conversion device and more specifically to a photoelectric conversion device in which a signal charge from a photoelectric conversion region that accumulates electric charges corresponding to incident light is inputted to a field effect transistor that is provided for amplification.
2. Related Background Art
FIG. 10A is a plan view showing the structure of a conventional CMOS sensor, and FIG. 10B is a schematic sectional view taken along the line 10B-10B of FIG. 10A. As shown in FIGS. 10A and 10B, a photodiode 1003 is formed in a p-well 1004. Electric charges accumulated in the photodiode 1003 are sent to a floating diffusion region 1011 and to a gate of a MOS transistor 1007, which is connected to the floating diffusion region 1011, when the electric potential of a transfer electrode 1006 is set to the high level. The MOS transistor 1007 amplifies the electric charges to output signals. As shown in FIG. 10B, the photodiode 1003 adjoins to a photodiode 1010 of an adjacent pixel and to a drain region 1005 of the MOS transistor 1007, with a selectively oxidized film 1001 separating the photodiode 1003 from 1010 and 1005. Note that a MOS transistor for reading electric charges accumulated in the photodiode 1010 is omitted from FIGS. 10A and 10B. There is a junction between the photodiode 1003 and the p-well 1004, and of electrons and holes generated by irradiation of light, the electrons are accumulated in the photodiode 1003 whereas the holes are discharged toward a substrate 1008. The photodiode 1003 is sandwiched between the p-well 1004 and a p+ region that is on the front side, constituting a buried photodiode.
In the device structure that uses the selectively oxidized film 1001, when the photodiode 1003 reaches saturation, electrons seep into the adjacent pixel (the photodiode 1010 in this example) instead of the drain region, causing cross talk.
Denoted by 1002 is a channel stopper under the selectively oxidized film 1001.
This device structure is contrasted by one disclosed in, for example, Japanese Patent Application Laid-Open No. 2000-260971, in which a photodiode is surrounded by diffusion layers or the like that are connected to a power source to make the diffusion layers double as a lateral overflow drain (LOD). However, this is an insufficient solution because carriers to be collected are also taken into the drain regions, thus lowering the efficiency.